Registration form – adding extra fields

I have installed BBPress, in my current registration page I have the code [bbp-register] which works and lets a user register. However the only fields here are to choose a username and enter email, where an password is automatically sent. What I need is to have an password field which the user enters, rather than having a generated one. I would also like other custom fields such as gender and age.

The form is located in form-user-register.php

Its fine to add the extra input boxes here and display, but I don’t know how these would get stored and saved.

Any help on how to make the custom fields save and which files to look at would be extremely helpful.